Regarding the super only (not the flow frames), what sort of performance have folks seen when using the modified Flow super through the winter? I’m in US zone 7, and I’m leaning away from leaving the modified super on all winter, since it’s not as weather-proof as a regular super. I’d still like to have a viewing window to peek in the hive, but do modified supers w/ windows over-winter well?

I’m just a first year keeper with a Flow hive myself, but I’d say with certainty that the Flow super is not meant to be used in an overwintering setup. The bees would propolise all the seams around the cutouts, and make your harvesting a bit tricky for next year